1, Field of the Invention
The present invention relates to a brushless DC motor structure and more particularly to a motor with an improved structure for a permanent magnet wound by a feeder coil and a fixed magnet bobbin.
2, Description of the Prior Art
Recently, in order to provide more functional equipment at lower cost, it has become normal to use the sectional drive method, in which a single equipment uses a plurality of dedicated motors, each serving a particular function. Particularly, in the case of small DC motors, light weight, enhanced magnetic circuit efficiency giving better motor efficiency to respond to required applications, diminished cogging torque and electromagnetic noise, and superior controllability are desired. Measures adopted so far to meet these demands include increasing the number of slots of the core, and increasing the number of poles of the magnet in order to improve the electromagnetic efficiency by shortening each magnetic circuit. Further, the winding efficiency of the coil is increased by using concentrated winding on a single salient pole, and at the same time, by using a powerful samarium-cobalt magnet as the permanent magnet.
The customary structure, used for the design of cores for brushless DC motors having cores laminated in the direction of the rotor shaft, has slots to hold the coils and yoke sections to form the magnetic paths (in a concentrated winding, the sections, hereafter called salient poles, which oppose the magnet acting through the medium of the air gap). Thin cores are laminated in multiple layers, insulation is applied to the necessary parts of the slots of the cores, and the coils are wound to form the armature. The feature of this construction is that each core is electrically insulated and iron loss is comparatively small.
However, with a laminated structure, if the number of salient poles of the core and the number of magnetic poles of the magnet are increased, the reduction in space between windings tends to cause a significant reduction in motor efficiency. Also, unless the size of the motor is increased, it is not possible to achieve the required volume of winding, and so a permanent magnet with high magnetic characteristics is employed to achieve the desired motor characteristics, despite the hi-her costs that result.
The present invention has been accomplished in view of the above-mentioned problems and it is an object of the invention to provide a brushless DC motor construction which is highly functional, generates little electromagnetic noise, uses an inexpensive magnet and does not employ a laminated structure stacked in the direction of the rotor shaft.